factory.js (1847B)
1 /** 2 * @license Apache-2.0 3 * 4 * Copyright (c) 2018 The Stdlib Authors. 5 * 6 * Licensed under the Apache License, Version 2.0 (the "License"); 7 * you may not use this file except in compliance with the License. 8 * You may obtain a copy of the License at 9 * 10 * http://www.apache.org/licenses/LICENSE-2.0 11 * 12 * Unless required by applicable law or agreed to in writing, software 13 * distributed under the License is distributed on an "AS IS" BASIS, 14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 15 * See the License for the specific language governing permissions and 16 * limitations under the License. 17 */ 18 19 'use strict'; 20 21 // MODULES // 22 23 var isNonNegativeInteger = require( '@stdlib/math/base/assert/is-nonnegative-integer' ); 24 var constantFunction = require( '@stdlib/utils/constant-function' ); 25 var isnan = require( '@stdlib/math/base/assert/is-nan' ); 26 var pow = require( '@stdlib/math/base/special/pow' ); 27 28 29 // MAIN // 30 31 /** 32 * Returns a function for evaluating the probability mass function (PMF) for a geometric distribution with success probability `p`. 33 * 34 * @param {Probability} p - success probability 35 * @returns {Function} PMF 36 * 37 * @example 38 * var pmf = factory( 0.5 ); 39 * var y = pmf( 3.0 ); 40 * // returns 0.0625 41 * 42 * y = pmf( 1.0 ); 43 * // returns 0.25 44 */ 45 function factory( p ) { 46 if ( 47 isnan( p ) || 48 p < 0.0 || 49 p > 1.0 50 ) { 51 return constantFunction( NaN ); 52 } 53 return pmf; 54 55 /** 56 * Evaluates the probability mass function (PMF) for a geometric distribution. 57 * 58 * @private 59 * @param {number} x - input value 60 * @returns {Probability} evaluated PMF 61 * 62 * @example 63 * var y = pmf( 2.0 ); 64 * // returns <number> 65 */ 66 function pmf( x ) { 67 var q; 68 if ( isnan( x ) ) { 69 return NaN; 70 } 71 if ( isNonNegativeInteger( x ) ) { 72 q = 1.0 - p; 73 return p * pow( q, x ); 74 } 75 return 0.0; 76 } 77 } 78 79 80 // EXPORTS // 81 82 module.exports = factory;